Construction sites are susceptible to rain delays that cost both time and money. When winter hits, project managers turn to the only proven method for site winterization, the process of chemically treating the surface soils to provide a high-strength and low- permeable cementitious barrier.
This type of treatment ensures immediate access to construction sites after a storm event, while eliminating fatigue rutting from repetitive loading. By reducing the permeability of the native soil, the treatment process reduces the susceptibility of the subgrade to saturation. An added benefit of this type of soil modification is the vast improvement of the subgrade strength characteristics and decreased potential for shrink/swell fluctuation of any clayey material. Since the construction process requires heavy loading from construction equipment, the subgrade soils are required to carry loads far greater than their design intended.
Winterization is the changing of soil behavior, principally through the reduction of excess moisture, in order to expedite construction. Winterization is commonly performed on subgrade and sub-base materials in order to expedite compaction and subsequent paving. A wide range of problem soils can be modified with various stabilizers to improve structural behavior. Included in this category are soils with:
Winterization may involve drying up construction sites and access roads regardless of the in-situ soil types. The common denominator for soil winterization is the improvement of soil behavior.
If drying is required for only a shallow depth (6”-12”), the subgrade soils can be treated and worked in place. Caution should be exercised, however, in areas where water has collected at greater depths. Such areas may require more treatment product mixed to greater depths (18”) for effective bridging.
The depth of modification needed to bridge over soft underlying soils is generally equivalent to the depth required to stabilize a subgrade by excavation, placement of a geofabric, and backfilling with aggregate.
When free water is encountered, an evaluation should be made to determine if water is infiltrating from an outside source. If the flow of water is continuous, dewatering will be required prior to any treatment. Dewatering should extend to at least 12 inches below the bottom of the treatment zone to reduce “wicking” of water. If it is determined that the water is only perched, areas containing any standing water should be pumped prior to treatment.
Contractor ingenuity and experience can usually be relied upon for the appropriate techniques to solve most job site variations. The services of a Geotechnical Engineer may be required, however, on the more complex projects and are recommended on “first-time” applications to determine performance goals.
Soil modification is an effective and economical technique that expedites construction with generally modest engineering requirements. In most instances, soil modification with various treatment products will correct adverse conditions immediately and permit construction activities to proceed on schedule.
The depth and percentage of treatment required for a particular project will be dependent upon when treatment is performed relative to the grading operations. The following are various sequences to consider when planning winterization protection for your project:
Treating before winter rains hit typically is the most economical choice. Pre-winter treatments require a lower percentage of stabilizing reagent and a shallower depth of treatment. This process creates an impervious liner at the surface grade that prevents winter rains from saturating the underlying soils.
Early treatments run the risk of being undermined by continued grading operations that may reduce the thickness of the section or overstress thinner sections by channel loading with heavy equipment.
When deciding pre-winter treatments, the project manager will be required to determine if the winterization protection can be incorporated into ongoing grading operations and if additional strength requirements should be incorporated.
Early treatment is best used for established grades or temporary access and haul roads.
An essential and timely use for treatment is during the installation of deep utilities. Excavating deep utilities is carried out with excavators capable of accessing sites in winter conditions. What becomes compromised during the winter months is the backfill material required once the pipes have been installed. Typically, these materials are left exposed during storm events or are excavated wet because of ground water.
These materials can easily be treated in an adjacent mixing table and used as backfill at anytime during the winter months.
In order to realize the full benefits of soil treatment for winterization, it's imperative to maintain as much of the treated section as possible during construction. Once deeper utilities have been installed and only shallow utilities remain, it would make economic sense to treat at rough subgrade elevation, which allows for shallow utility installation and general site access.
The most economical and beneficial winterization treatment is one that performs as a subgrade design feature. The engineering benefits of treating at subgrade elevation are an increase in the measured strength (R-Value and Unconfined Strength) of the subgrade soil. This concept allows for a permanent structural foundation under the new pavement. This foundation is desirable since the pavement's life-cycle is diminished when native subgrades become saturated over time.
When engineers incorporate this treated section into their overall design, the aggregate base layer of the pavement may be reduced, thus reducing the overall cost of the roadway construction.
The winterization process should also be incorporated into the Storm Water Pollution Prevention Plan. The best winterization treatment plan can also prevent storm water pollution, since soil stabilization has been utilized in Water Resource projects as a method of erosion prevention and impervious soil lining for water retention facilities.